A variety of methods have been known as a method of producing a preform of a reinforcing fiber such as a glass fiber or a carbon fiber used for manufacture of a fiber-reinforced plastic. For example, a known method cuts out a predetermined cut pattern from a fabric such as a woven fabric base material of reinforcing fiber and produces a preform by pressing the cut pattern. That method, however, causes a residual part of the woven fabric base material after cutting out the cut pattern to be wasted. This causes a problem of decreasing the yield in production of the preform and increasing the production cost of the preform.
To avoid this problem, AFP (automated fiber placement) and TFP (tailored fiber placement) methods have been known with a view to placing reinforcing fibers in only required locations and reducing the waste of reinforcing fibers. For example, as shown in FIG. 1, JP 2011-57767 A discloses a method that places strands of a reinforcing fiber mixed with a binder (reinforcing fiber bundle 14) on a preform-forming tool by a movable accumulation head 2 and sequentially repeats this placement operation upward to form a plurality of layers and produce a preform. JP 2011-515242 A discloses a method that places a plurality of parallel composite tape strips in only required locations while moving an automated fiber placement head on a base plate, as the method of forming a composite layered product on the base plate.
The above techniques, however, have two problems. In an apparatus that employs either of the methods of JP '767 and JP '242 described above, for example, as shown in FIG. 1, a cutting mechanism 11 configured to cut a reinforcing fiber bundle 14 is mounted in a head 2 configured to supply the reinforcing fiber bundle 14. The first problem is accordingly that the reinforcing fiber bundle is cut while being separated from the head at a high speed.
Continuously applying a force such as shear force at one point of a cutting object is generally required for cutting. When the cutting object moves at a high speed, however, there is a difficulty in ensuring a sufficient time period to apply the force at one point. This results in a difficulty in cutting. To solve this problem, the time period required for cutting should be minimized, and cutting should be completed instantaneously. For this purpose, there is a need to maximize the above force. For example, in cutting by shearing, it is required to maximize the shear force to increase the operation speed of a shear blade and apply a sufficient force for shearing in a short time period. The configuration that the cutting mechanism is mounted in the head, however, provides the structural restriction including the size, the weight and the location. Additionally, increasing the shear capacity results in increasing the equipment cost. There is thus naturally a limit on maximizing the shear force.
Especially the reinforcing fiber is likely to be not readily cut. Additionally, a plurality of fibers are likely to be handled at a time, with a view to increasing the production capacity of the apparatus. Both these factors significantly increase the time period required for cutting. It is accordingly difficult to complete cutting instantaneously.
Furthermore, moving the reinforcing fiber bundle during cutting causes a slight difference in cutting timing. Even when the reinforcing fiber bundle is cut at identical timings, this causes a difference in cutting position. When there is a difference in cutting position, a margin is set in expectation of a potential difference. Setting the margin, however, provides a need for trimming to a predetermined final shape. This increases the waste of reinforcing fiber and causes a low yield.
It could therefore be helpful to decrease the moving speed of the reinforcing fiber bundle during cutting of the reinforcing fiber bundle. This requires deceleration or stopping of the head to thereby cause reduction of the production capacity.
The second problem of the techniques disclosed in JP '767 and JP '242 is as follows. As shown in FIG. 1, a pressing roller 6 configured to place the reinforcing fiber bundle 14 is provided at an end of the head 2 configured to supply the reinforcing fiber bundle. It is required to feed a portion of the reinforcing fiber bundle 14 upstream of the cutting mechanism 11 to the pressing roller 6 every time the reinforcing fiber bundle 14 is cut off. In both the apparatuses of JP '767 and JP '242, as shown in FIG. 1, the cutting mechanism 11 for the reinforcing fiber bundle 14 is placed on the front side of the end of the head 2 where the pressing roller 6 is provided, i.e., on the slightly upstream side of the end of the head that corresponds to the most downstream side of the reinforcing fiber bundle 14 in the viewpoint of the moving direction of the reinforcing fiber bundle 14. When the reinforcing fiber bundle 14 is cut in this configuration, a portion of the reinforcing fiber bundle 14 downstream of the cutting position of the reinforcing fiber bundle 14 is fully placed on the forming tool or the base plate by the pressing roller 6. This causes no reinforcing fiber bundle 14 to be present from the cutting position of the reinforcing fiber bundle 14 in the head 2 to the end of the head 2. To repeat the operation of placing the reinforcing fiber bundle 14 on the forming tool or the base plate, there is accordingly a need to feed the reinforcing fiber bundle 14 to the end of the head 2 by some method. This method may be, for example, a method of feeding the reinforcing fiber bundle by nip rolls or a method of sucking and pulling the reinforcing fiber bundle by the air. Both the apparatuses of JP '767 and JP '242 are equipped with a mechanism of feeding the reinforcing fiber bundle. This mechanism increases the equipment cost and also decreases the production capacity due to a need for an extra time for feeding the reinforcing fiber bundle.